This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-254667, filed Aug. 24, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a production process of an optical disk with two layers on one side using an ultraviolet curing resin (2P resin: Photo-Polymer) and an optical disk produced thereby.
2. Description of the Related Art
Various methods have been employed to make a high capacity optical disk. One method is for making a disk on which one side was doubly layered, as shown in Japanese Patent Application Laid-Open No. 10-283682. A process for producing the optical disk using an ultraviolet curing resin (hereinafter, described as 2P resin) which is cured with ultraviolet rays, is adopted as the present production process of an optical disk with two layers on one side.
The production process is explained below. Firstly, a semi-transparent film is formed on a molded substrate on which a pattern for the first layer was transcribed. A 2P resin is coated on the first layer, a nickel stamper is pushed on the 2P resin, ultraviolet rays are irradiated to cure the 2P resin, and then the second layer is transcribed.
The prior art is characterized in that in order to avoid peeling the 2P resin from the first layer when peeling the stamper from the 2P resin, an adhesive layer is provided between the 2P resin and the first layer.
It is assumed that the prior art first generation DVD (Digital Versatile Disk) is subject to the incidence of laser light from a molded substrate side. The prior art DVD adopts a process in which the first layer on the molded substrate is semi-transparent and the 2P resin is sandwiched by a nickel stamper, and ultraviolet rays are irradiated to cure it.
However, the side which receives the incidence of laser light is opposite the side of the molded substrate in the next generation DVD, therefore it is the opposite side of the first generation DVD. Accordingly, the total reflection film of the second layer is formed on the molded substrate, and if the 2P resin is sandwiched by the nickel stamper, the 2P resin cannot be cured because ultraviolet rays are not transmitted through the total reflection film.
Japanese Patent Application Laid-Open No. 4-372741 shows a transparent quartz stamper, but the quartz must be prepared by an etching process in order to make the stamper which cannot be prepared in the usual production process of an optical disk. Therefore, a special facility is required.
Namely, according to the conventional production process of a two layered optical disk using the 2P resin, when the total reflection film is provided as the film on the molded substrate side, the 2P resin is sandwiched by the opaque total reflection film and the nickel stamper. Therefore, even if ultraviolet rays are used, they cannot reach the 2P resin. Accordingly, the conventional production process of an optical disk has a problem in that the 2P resin of the next generation optical disk with two layers on one side cannot be cured by ultraviolet rays.
Further, since a step of etching quartz or the like is necessary to form a stamper in the conventional production process of the optical disk, the stamper is not prepared in the usual production process of an optical disk, and a special facility with a high cost is required. Therefore, there is a problem in that the stamper cannot be easily produced and prepared in large quantities.
An object of the present invention is to easily produce the next generation optical disk with two layers on one side by forming a transparent stamper by injection molding, which is the production process of an optical disk, preparing a semi-transparent stamper obtained by depositing a semi-transparent metal thin film on the transparent stamper, and using the semi-transparent stamper during curing of the 2P resin by ultraviolet rays.
Another object of the present invention is the production process of an optical disk, wherein when forming a layer of an ultraviolet curing resin, which constitutes a portion of the optical disk, a semi-transparent film of a metal is formed on a molded substrate upon which a pattern was transcribed, and this molded substrate is used as a semi-transparent stamper.
According to an object of the present invention, since the stamper is a semi-transparent stamper prepared from a resin, it transmits ultraviolet rays which the nickel stamper of a conventional apparatus does not transmit. Even if the total reflection film of a metal is formed on a molded substrate as the next generation optical disk, and ultraviolet rays cannot be irradiated from the substrate side, the ultraviolet rays are irradiated through the semi-transparent stamper and the 2P resin can be cured. Further, since the semi-transparent stamper can be prepared in one process of injection molding, which is the production process of an optical disk, disposable semi-transparent stampers can be easily produced in large quantities. Accordingly, it is advantageous from the viewpoint of cost, that a stamper in an optimum condition be utilized and the efficient production of an optical disk can be carried out.
Further, another object of the present invention is an optical disk having an ultraviolet curing resin layer, including at least a first substrate; a first metal thin film layer formed on the first substrate; and a layer of the ultraviolet curing resin formed on the first metal thin film layer and cured by irradiation of ultraviolet rays through a semi-transparent stamper having a semi-transparent metal film formed on a transparent molded substrate having a pattern transcribed thereon.
According to an embodiment of the present invention, the optical disk is a next generation optical disk with two layers on one side, but since the semi-transparent stamper, obtained by forming a semi-transparent metal film on a transparent molded substrate having a pattern transcribed thereon, is used, the 2P resin, which is an ultraviolet curing resin, which could not be used in conjunction with a conventional nickel stamper, can be used even if the optical disk has the structure of two layers on one side. Thus, an optical disk can be provided having high reliability while suppressing costs for a stamper.